1. Field of the Invention
The present invention is directed toward the field of manufacturing integrated circuits.
2. Description of the Related Art
When manufacturing integrated circuits, deposition processes are employed to deposit thin layers of insulative material and conductive material onto wafers. Deposition has been performed through various well known deposition processes, such as chemical vapor deposition ("CVD") and physical vapor deposition ("sputtering").
In a CVD process, a wafer is loaded into a chemical vapor deposition chamber. A vapor of a metallo-organic compound, such as tetrakis (dimethylamido) titanium (TDMAT), which has the formula Ti(N(CH.sub.3).sub.2).sub.4, is loaded into the chamber and infused with energy. The energy is generated through such means as a thermal heat source, in the case of thermal CVD, or a radio frequency ("rf") signal source, in the case of plasma enhanced CVD. The energized chemical vapor reacts with the wafer's surface to form a thin layer of material on the wafer. When the TDMAT chemical vapor is used, a titanium nitride film is deposited on the wafer's surface.
In a sputtering process, a wafer is placed in a physical vapor deposition ("PVD") chamber, and the chamber is filled with a gas, such as argon. A plasma containing positively charged ions is created from the gas, by creating an electrical field in the chamber. The positively charged ions accelerate and collide into a target material, which is mounted in the chamber. Atoms of the target material are thereby separated from the target and deposited on the wafer to form a layer of target material on the surface of the wafer.
In order to enhance the bombardment of the target material by the positively charged ions in a traditional sputtering process, a negative bias may be provided to the target material. This is achieved by providing a radio frequency signal to an electrode that supports the target material. In order to facilitate the generation of the positively charged ions in a high density plasma PVD chamber, a separate rf signal may also be inductively coupled to the PVD chamber. In such a high density plasma PVD chamber, yet another rf signal may be provided to a pedestal that supports the wafer in the PVD chamber to improve attraction of the target material to the wafer.
A deposition chamber, such as a CVD chamber or a PVD chamber, may be used to deposit diffusion barriers in an integrated circuit. Diffusion barriers are employed in integrated circuits to prevent diffusion of a contact metal, such as aluminum, into the active region of a semiconductor device built on a silicon substrate. Unlike an insulative layer of material, a diffusion barrier is employed where it is desirable to have a conductive path for current to flow between the contact metal and the active semiconductor region. For example, a diffusion barrier may be employed to overlie a silicon substrate at the base of a contact hole to prevent interdiffusion of a contact metal, which fills the contact hole, into the substrate.
A severe interdiffusion between a contact metal, such as aluminum, and a silicon substrate can begin to take place when the integrated circuit is heated to temperatures in excess of 450.degree. C. If an interdiffusion is allowed to occur, the aluminum contact metal penetrates into the silicon substrate, thereby causing an open contact in the integrated circuit and rendering it defective.
FIG. 1 illustrates a diffusion barrier 100 that resides between a conductive region 105 of a silicon substrate 101 and a contact plug 102. A contact hole 103 is formed in an insulative layer of material 104, such as silicon dioxide, that overlies the substrate 101. The diffusion barrier 100 is ideally formed so that it is thin and substantially conforms to the contours of the surface of the contact hole 103.
If the diffusion barrier 100 is thin and highly conformal, the contact metal 102 is able to form a sufficiently conductive ohmic contact with the silicon substrate's conductive region 105. If the diffusion barrier 100 is too thick or poorly formed, as shown in FIG. 2, it will prevent the contact metal 102 from forming a sufficiently conductive ohmic contact with the substrate region 105. In FIG. 2, the poorly formed diffusion barrier 100 severely narrows the opening of the contact hole 103, which causes the contact metal 102 to form so that it does not reach the base of the contact hole 103, and a void 106 is created.
In order to ensure a good ohmic contact between the contact metal 102 and the substrate region 105, it is desirable for the resistance of the diffusion barrier 100 be minimal. Typically, a resistivity value of 1,000 .mu..OMEGA.-cm or less is acceptable One material that has been successfully employed as a diffusion barrier is titanium nitride (TiN).
However, in some deposition processes, such as those using TDMAT, the resistivity of the titanium nitride barrier layer is high and unstable. This is partly because a significant fraction of the deposited barrier material is composed of a carbon (hydrocarbons, carbides, etc.) and because the titanium, a chemically reactive metal, may not be completely reacted in the film. Accordingly, it would be desirable to treat such a layer of barrier material with a post-deposition processing, so that its resistivity was reduced and stabilized.
In manufacturing an integrated circuit, it is desirable to perform successive steps of the manufacturing process, such as deposition and post-deposition processing, in the same chamber ("in-situ"). In-situ operations reduce the amount of contamination that a wafer is exposed to by decreasing the number of times that the wafer is required to be transferred between different pieces of manufacturing equipment. In-situ operations also lead to a reduction in the number of expensive pieces of manufacturing equipment that an integrated circuit manufacturer must purchase and maintain.
In the fabrication of integrated circuits, there has been an increased use of aluminum metalization processes operating at high temperatures, in excess of 450.degree. C. This has made it desirable to have diffusion barriers with a greater ability to inhibit the diffusion of contact metals, such as aluminum. Traditionally, diffusion barriers have been made thicker, in order to accommodate such a desire. However, smaller geometries are also being employed in the fabrication of integrated circuits, thereby decreasing the dimensions of contact holes and making it desirable for diffusion barriers to become thinner and more conformal.
Accordingly, it would be desirable to be able to construct a highly conformal thin diffusion barrier with an increased ability to inhibit the diffusion of contact metals, such as aluminum Additionally, it is desirable for such a diffusion barrier to not have a resistance that is greatly increased over the resistance of traditional diffusion barriers. It would also be desirable to construct such a diffusion barrier in-situ.